It has been so many years since M$ started a CFS4 I can not remember when it was. However, they canceled it and have disbanded Aces the team that built the CFS series and there will never be a M$ CFS4.

M$ is only interested in large profit programing and sims are break even make a little money things. IL-2 did OK as has the Silent Hunter WWII submarine/u-Boat series (even better than they hoped)
100K sales of a game is the minimum to consider doing another and sims are low volume programs that people like us use for way too long without needing to buy something else from the developer.